The present invention relates generally to the field of automatic loading and unloading material movers. More particularly, the present invention relates to a mover wherein material is loaded and unloaded on a vehicle by having the floor of a tiltable bed of the vehicle move in a direction opposite to the direction of movement of the vehicle. The present invention is specifically described with respect to loading and unloading agricultural products such as cotton modules, but the principles involved are also applicable to other heavy materials.
An automatic loading/unloading material mover typically consists of a wheeled vehicle having a tiltable bed with a moving floor. Sometimes, the floor of the bed is powered by one or more hydraulic motors. For loading, the vehicle is backed into position next to a cotton module, for instance, and the bed of the vehicle is tilted so that the back edge of the bed touches or is in close proximity to the ground near the cotton module. Then, the vehicle slowly travels in reverse so that the tilted bed is forced underneath the cotton module At the same time, the floor of the tilted bed moves in the direction opposite that of the vehicle. This causes the cotton module to progress up the bed towards the front of the vehicle. Once the module is loaded on the bed of the vehicle, the bed is tilted back to a horizontal position and the module can be moved to a different location. To unload a module, the operation is reversed. The bed is tilted from its horizontal position until the back of the bed again touches the ground or is in close proximity to the ground. The vehicle then moves forward and the floor of the bed moves backwards. This causes the module to progress down the tilted bed and onto the ground.
It can be seen from the preceding description that it is important that the floor of the bed maintain a fixed position relative to the ground so that the module being unloaded or loaded is not jolted or pulled apart.
The prior art has several types of systems that attempt to control the speed of the bed floor so that it equals the speed of the vehicle. The most common prior art system uses a gauge wheel which engages the ground when the tiltable bed is inclined in the loading/unloading position. The speed of this gauge wheel along the ground is used to monitor the speed of the vehicle. This information is then used to control the speed of the bed floor, sometimes called a conveyor. The accuracy of this control system, however, is limited by the accuracy of the gauge wheel and the accuracy of the gauge wheel is greatly affected by the terrain. For instance, on muddy or slippery ground, the gauge wheel slips and does not provide an accurate indication of the speed of the vehicle. Since slippery ground is quite common in agricultural settings, these systems are sometimes not accurate enough to prevent damage to the module being loaded or unloaded due to the differences in the vehicle speed and the bed floor speed. A typical prior art system of this type is shown in U.S. Pat. No. 4,243,353 (Reed).
Another type of prior art synchronization system includes a roller which engages a non-driven wheel of the vehicle and rotates at a speed proportional to the vehicle velocity. This roller provides a signal which is used to synchronize the velocity of the bed floor. Again, however, the accuracy of this system is limited by the need for the roller to be maintained in very firm, non-slipping contact with the non-driven vehicle wheel. In agricultural conditions, this is often times not possible and hence the accuracy of the synchronization system suffers. This type of prior art system is shown in U.S. Pat. No. 4,081,094 and Reissue U.S. Pat. No. 30,404 (Pereira).
Another type of synchronization system is shown in U.S. Pat. No. 4,441,848 (Bailey). This system uses magnetic sensing on a non-driven wheel of the vehicle to determine the velocity of the vehicle. A magnetic sensor generates an alternating output voltage which is used to determine the velocity of the vehicle. A similar magnetic sensing system is used to determine the velocity of a conveyor belt on the bed of the vehicle. The vehicle speed and the conveyor belt speed are then compared in an analog fashion and the speed of the conveyor belt is adjusted accordingly. This system, while probably more accurate than those systems using a gauge wheel, still suffers from errors at the low speeds that are necessary during the load/unload process. At these very low vehicle speeds, it is quite difficult to accurately measure the velocity of the vehicle by processing the alternating output voltage received from the magnetic sensor. Likewise, any other method of measuring velocity, such as radar or sonar at these low speeds of the truck also provide inaccurate results. Furthermore, any errors produced in the speed measurement of either the vehicle or the bed floor are accumulated during the entire process.
The present invention provides an extremely accurate system for synchronizing the movement of the bed floor to the movement of the vehicle.